(1) Field of the Invention
The present invention relates generally to narrow groove welding and, more particularly, to a narrow groove welding apparatus with replaceable gas cups so that the apparatus can be used to weld grooves of different depths.
(2) Description of the Prior Art
Narrow groove welding can be defined as the welding of opposed faces of two metal parts that are separated by narrow space in the form of a groove, which may have a depth of 5 inches or more. The angle of the groove is kept small to minimize the amount of welding required, and thus the time involved.
In narrow groove welding a nonconsumable electrode mounted in a carrier is inserted into the groove between parts to be welded, with the end of the electrode being spaced from the area being welded, i.e., the weld zone, at a predetermined distance. An electrical current forms an arc between the electrode tip and the work piece, and a consumable wire is fed into the weld zone to provide material to fill the groove. To avoid oxidation of the metal parts during welding, the electrode is surrounded by a spaced annular housing, or gas cap, and an inert covering gas, e.g., argon or a mixture of argon and helium, is fed between the housing and electrode and out of an opening in the bottom of the gas cup to create a gas blanket over the weld zone.
The electrode carrier, the gas cup, and related components, including a torch block for mounting the electrode carrier and the gas cup, are together referred to as the torch assembly. In automatic or semi-automatic welding, the torch assembly is carried along a set pathway by a motorized weldhead or transport mechanism, with the torch being vertically positionable on the weldhead. As the groove is filled, the torch assembly is raised to properly position the electrode tip in relation to the weld zone. In addition, torch assemblies are known in the prior art in which the gas cup can be replaced with a gas cup of a different length, so that progressively shorter gas cups can be used as the groove is filled.
Replacement of the gas cup requires a corresponding replacement of the electrode of a different length, or an adjustment in the vertical length of the existing electrode so that the tip of the electrode projects the desired distance from the gas cup. Electrode replacement is also required due to electrode erosion or wear. Depending on amperage, this may need to be done as often as once per arc-hour.
Narrow groove welding apparatuses are also known to include a visual monitoring mechanism, such as a fiberscope or lens in the vicinity of, and directed toward, the weld zone so that the operator can monitor the condition of the weld. The monitoring mechanism may also include a light source to illuminate the weld when welding is not taking place. Weld monitoring mechanisms per se are known in the prior art as exemplified by U.S. Pat. Nos. 4,581,518 to Takahashi et al, and 5,475,198 to Burke et al.
Replacement of gas cups in prior art welding apparatus has been difficult and time consuming. In addition, adjustment of the electrode position to the proper length has been cumbersome, and has exposed the operator to the welding environment for a lengthy period of time. Finally, there has been no convenient means for repositioning auxiliary components so that they are directed toward the weld zone after replacement of the gas cup with a gas cup of a different length.
Thus, there remains a need for a new and improved narrow groove welding apparatus which provides for ready replacement of welding torch gas cups and electrodes of a length corresponding to the gas cup length while, at the same time, also provides for quick positioning of auxiliary components to accurately direct the components toward the welding zone.
The present invention is also directed to a new and improved torch assembly including a replacement electrode carrier in which the electrode is pre-positioned to a predetermined height matching the replacement gas cup, thus allowing the operator to quickly replace the previous electrode with an electrode of the proper length when changing gas cups. The torch assembly also includes insulators for electrically isolating the electrode from the gas cap, thus preventing arcing between the gas cup and the workpiece.